Well, here's what I'm being told by HP. There switches support LLDP which, like stated above, is IEEE standards based discovery. New Cisco phones would be PoE supported and I was told by switch engineers that they could not forsee any issue; however, they were not well versed in regards to Cisco Call Manager.
Then I called Cisco and talked to a "voice engineer". The Cisco phones support LLDP-MED a subset of LLDP along with CDP. Also, FYI, the Catalyst switches support LLDP for compatibility connecting to 3rd party switches. The Cisco engineer also stated that there would not be any issue in using HP switches siting examples of using Cisco IP Phones with other IP Telephony vendors hardware. His main statement to me was that whatever switch was deployed that it support QoS, VLAN, and 802.3af PoE; I'd be in good shape.
When I asked both engineers for maybe a reference or case study I could draw from, neither could help me. I feel like "BuckWeet" is correct that in another year or two, Cisco will be forced to be more standards based solidifying the ability to work with already deployed infrastructure. IPT is fairly more expensive right now but as more manufacturers come to market with product, prices should drop. I cannot foresee Cisco trying to penetrate and evolve the key/pbx market by requiring the utter and complete overhaul of most customer's network equipment when so many others like Avaya, Mitel, ShoreTel, etc...can take advantage of already deployed standards.
I just wish someone could give me a real world instance of this running.